Method of determining focus, inspection apparatus, patterning device, substrate and device manufacturing method

Abstract

A method of determining focus of a lithographic apparatus has the following steps. Using the lithographic process to produce first and second structures on the substrate, the first structure has features which have a profile that has an asymmetry that depends on the focus and an exposure perturbation, such as dose or aberration. The second structure has features which have a profile that is differently sensitive to focus than the first structure and which is differently sensitive to exposure perturbation than the first structure. Scatterometer signals are used to determine a focus value used to produce the first structure. This may be done using the second scatterometer signal, and/or recorded exposure perturbation settings used in the lithographic process, to select a calibration curve for use in determining the focus value using the first scatterometer signal or by using a model with parameters related to the first and second scatterometer signals.

The invention claimed is: 
     
       1. A method comprising:
 using first and second structures, on a substrate, having respective first and second exposure dose sensitivities to an exposure dose of a litholgraphic apparatus, the first and second exposure dose sensitivities being different from each other; 
 detecting scattered radiation from the first structure; 
 obtaining a first scatterometer signal based on the detected scattered radiation from the first structure; 
 measuring an asymmetry of the first structure based on the obtained first scatterometer signal; and 
 determining a focus value of the lithographic apparatus used to produce the first structure based on the measured asymmetry of the first structure, an exposure perturbation parameter used to produce the first structure, and a property of the second structure. 
 
     
     
       2. The method of  claim 1 , further comprising using an exposure dose for the exposure perturbation parameter. 
     
     
       3. The method of  claim 1 , further comprising using an aberration for the exposure perturbation parameter. 
     
     
       4. The method of  claim 1 , further comprising:
 detecting scattered radiation from the second structure; 
 obtaining a second scatterometer signal based on the detected scattered radiation from the second structures; and 
 determining the focus value based on the second scatterometer signal. 
 
     
     
       5. The method of  claim 4 , further comprising:
 using a mirrored configuration of the first structure for the second structure; 
 using a magnitude and sign for the first exposure dose sensitivity that is equal and opposite to a magnitude and sign of the second exposure dose sensitivity, respectively; and 
 determining the focus value based on a difference between the first scatterometer signal and the second scatterometer signal. 
 
     
     
       6. The method of  claim 4 , further comprising:
 using a lithographic process to produce the first structure on the substrate, the first structure having at least one feature asymmetry that depends on focus and exposure perturbation parameters of the lithographic apparatus; and 
 using the lithographic process to produce the second structure on the substrate, the second structure having at least one feature form that depends on the focus and exposure perturbation parameters of the lithographic apparatus, 
 wherein the dependence of the at least one feature asymmetry on the focus and exposure perturbation parameters is different from the dependence of the at least one feature form on the focus and exposure perturbation parameters. 
 
     
     
       7. The method of  claim 6 , further comprising simultaneously performing the using of the lithographic process to produce the first and second structures. 
     
     
       8. The method of  claim 4 , wherein the detecting of the scattered radiation from the first and second structures comprises using image plane detection scatterometry. 
     
     
       9. The method of  claim 4 , wherein the detecting of the scattered radiation from the first and second structures comprises using pupil-plane detection scatterometry. 
     
     
       10. The method of  claim 4 , further comprising simultaneously performing the detecting of the scattered radiation from the first and second structures. 
     
     
       11. The method of  claim 1 , further comprising:
 detecting scattered radiation from the second structure; 
 determining a second scatterometer signal based on the detected scattered radiation from the second structure; 
 measuring an asymmetry of the second structure based on the second scatterometer signal; and 
 determining the focus value based on the measured asymmetry of the second structure. 
 
     
     
       12. The method of  claim 4 , wherein the determining of the focus value comprises selecting a calibration curve based on the second scatterometer signal. 
     
     
       13. The method of  claim 4 , wherein the determining of the focus value comprises using a model with parameters related to the first and second scatterometer signals. 
     
     
       14. The method of  claim 1 , further comprising determining the exposure perturbation parameter used to produce the first structure. 
     
     
       15. The method of  claim 1 , further comprising receiving information related to the exposure perturbation parameter used to produce the first structure. 
     
     
       16. The method of  claim 15 , further comprising applying exposure perturbation corrections during production of the first structure using a lithographic process based on the received information. 
     
     
       17. The method of  claim 15 , wherein the determining of the focus value used to produce the first structure comprises selecting a calibration curve based on the received information. 
     
     
       18. The method of  claim 1 , further comprising:
 receiving information related to focus used to produce the first structure; and 
 determining the focus value used to produce the first structure based on the received information. 
 
     
     
       19. The method of  claim 18 , further comprising applying focus corrections during production of the first structure using a lithographic process based on the received information. 
     
     
       20. An inspection apparatus comprising:
 an illumination system configured to illuminate first and second structures produced on a substrate using a lithographic apparatus, the first and second structures having respective first and second exposure dose sensitivities to an exposure dose of the lithographic apparatus, the first and second exposure dose sensitivities being different from each other; 
 a detection system configured to:
 detect scattered radiation from the first structure, and 
 obtain a first scatterometer signal based on the detected scattered radiation; and 
 
 a processor configured to determine a focus value used to produce the first structure based on an asymmetry of the first structure, an exposure perturbation parameter used to produce the first structure, and a property of the second structure. 
 
     
     
       21. The inspection apparatus of  claim 20 , wherein the exposure perturbation parameter comprises exposure dose. 
     
     
       22. The inspection apparatus of  claim 20 , wherein the exposure perturbation parameter comprises aberration. 
     
     
       23. The inspection apparatus of  claim 20 , wherein:
 the illumination system is further configured to illuminate the second structure; 
 the detection system is further configured to:
 detect scattered radiation from the second structure, and 
 
 obtain a second scatterometer signal based on the detected scattered radiation from the second structure; and 
 the processor is further configured to determine the focus value based on the second scatterometer signal. 
 
     
     
       24. The inspection apparatus of  claim 23 , wherein:
 the first structure comprises a mirrored configuration of the second structure; 
 the first exposure dose sensitivity comprises a magnitude and sign that is equal and opposite to a magnitude and sign of the second exposure dose sensitivity, respectively; and 
 the processor is further configured to determine the focus value used to produce the first structure based on a difference between the first scatterometer signal and the second scatterometer signal. 
 
     
     
       25. The inspection apparatus of  claim 23 , wherein the processor is further configured to:
 select a calibration curve based on the second scatterometer signal; and 
 determine the focus value based on the selected calibration curve. 
 
     
     
       26. The inspection apparatus of  claim 25 , wherein the processor is further configured to determine the focus value based on a model with parameters related to the first and second scatterometer signals. 
     
     
       27. The inspection apparatus of  23 , wherein the processor is further configured to determine the exposure perturbation parameter used to produce the first structure. 
     
     
       28. The inspection apparatus of  20 , wherein the processor is further configured to receive information related to the exposure perturbation parameter used to produce the first structure. 
     
     
       29. The inspection apparatus of  claim 28 , wherein the processor is further configured to apply exposure perturbation corrections during production of the first structure using the lithographic process based on the received information. 
     
     
       30. The inspection apparatus of  claim 28 , wherein the processor is further configured to:
 select a calibration curve based on the received information; and 
 determine the focus value used to produce the first structure based on the selected calibration curve. 
 
     
     
       31. The inspection apparatus of  claim 20 , wherein the processor is further configured to:
 receive information related to focus used to produce the first structure; and 
 determine the focus value based on the received information. 
 
     
     
       32. The inspection apparatus of  claim 31 , wherein the processor is further configured to apply focus corrections during production of the first structure using the lithographic process based on the received information. 
     
     
       33. A method comprising:
 determining focus of a lithographic apparatus using a method comprising:
 using first and second structures, on a substrate, having respective first and second exposure dose sensitivities to an exposure dose of a lithographic apparatus, the first and second exposure dose sensitivities being different from each other, 
 detecting scattered radiation from the first structure, 
 obtaining a first scatterometer signal based on the detected scattered radiation from the first structure, 
 determining a focus value of the lithographic apparatus used to produce the first structure based on an asymmetry of the first structure, an exposure perturbation parameter used to produce the first structure, and a property of the second structure; and 
 
 controlling the lithographic apparatus for subsequent substrates based on a result of the determining of the focus of the lithographic apparatus.